Apparatus for receiving facsimile signals



Nov. 1, 1949.. c. J. YOUNG APPARATUS FOR RECEIVING FACSIMILE SIGNALS 2 Sheets-Sheet l Filed Oct. 3l, 1945 ATTORNEY Nov. 1, 1949. A c. J. YOUNG 2,486,511

APPARATUS FOR RECEIVING FACSIMILE SIGNALS Filed Oct. 31, 1945 2 Sheets-Sheet 2 mdium.

ATTORNEY Patented Nov. 1, 1949 APPARATUS FOR RECEIVING FACSIMILE SIGNALS Charles Jj Young, Princeton, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application October 31, 1945, Serial No. 625,891

9 Claims.

l The present invention relates to apparatus for receiving facsimile signals and more particularly, although not necessarily exclusively, to a novel larrangement for producing a record in accordance with frequency modulated image signals.

The principal object of the present invention is to provide recording apparatus for producing marks which will operate directly under the control of a frequency modulated signal, thereby obviating the need for the usual printer amplifier,

or the need for a discriminator or the like for de- 'and/or spacing signals of a given frequency. This result is accomplished without recourse to the phenomena of mechanical resonance so that marks produced in accordance with the invention are free or substantially free of a dot pattern.

Accordingly, another important object of the invention is to provide a recording unit capable of assuming a continuous operating condition so yas to exert substantially continuous recording pressure without recurring percussive effects when excited with alternating current of carrier frequency.

A further object of the invention is to provide a novel tape recorder which is responsive to signals of varying frequency.

Other objects and advantages of the present invention will, of course, become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following specification in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic showing of a transmitting station for providing signals which are frequency modulated in accordance with the scanning of a piece of subject matter;

Fig. 2 shows, illustratively, recording apparatus embodying the invention;

Fig. 3 shows a desired relationship of iilter response curves in accordance with the invention; Fig. 4 is a detail of the apparatus of Fig. 2;

Fig. 5 is a diagrammatic showing of a slight modification of the recording arrangement of Fig. 2; and

Fig. 6 shows a further modification of the receiving apparatus of the invention.

Referring to the drawings and more particularly to Figs. 1 and 2 thereof, a facsimile system is shown by way of example for transmitting and 'y lator indicated at 2l.

receiving signals derived as a result of scanning pictures, drawings, or other subject matter. The signals so derived and a carrier modulated with these signals will be referred to as image signals for the sake of brevity. The invention is concerned more particularly with a modulating system in which a characteristic of a carrier wave other than the amplitude, for example the frequency, is varied.

In Fig. 1 the subject copy is shown as being in the form of a tape I 2 bearing printed characters, or the like I4, which are to be scanned for the purpose of producing image signals for transmission to a more or less remote point for intelligence communication purposes. The tape I2 is guided on suitable rollers I5 and I6, one of which, roller I6, for example, may be power driven as shown through the medium of a motor I8 and a gear box 2| or the like containing suitable mechanism'to correlate the movement of the tape I2 with the rotation of a scanning element 22. The motor I8 may be of the alternating current synchronous type connected to an alternating current service connection I9. A light source such as an incandescent lamp 23 provides a spot of light on the tape which excites a photocell 24. A tape scanner generally of this type is shown in the United States Patent No. 2,222,937, granted to G. L. Dimmick on November 26, 1940. Other means for producing image signals as a result of scanning may of course be employed.

The image signals from the photocell 24 are ampliiied in an amplifier 26 and are employed to vary the frequency of a carrier wave in a modu- The output of the modulator is used in turn to modulate radio Waves produced and radiated from a radio transmitter 29. A suitable system having equipment such as that shown in Fig. l is disclosed in greater detail in the United States Patent No. 2,326,740, granted to Maurice Artzt on August 1'7, 1943.

A receiving station is shown in Fig. 2 of the drawings which includes a disclosure of recording apparatus embodying the invention in one form. A radio receiver 33, which includes a detector for recovering the intelligence bearing signal, such as is produced by the modulator 2`I of Fig. l, furnishes the recovered signal to an amplifier 34. It will be understood that the amplifier 34 may be included in the radio receiver 33 in the form of an audio amplier normally employed to operate a loudspeaker.

By way of example, the transmitting system so far described and the receiver 33 provide signals in the output of the amplier 34 the frequency of which varies in accordance with the light and dark areas on the subject copy, such as the tape l2, at the transmitter. The modulator 2'I of the transmitter may provide two signalling frequencies, for example, one of which appears when a dark portion of the subject copy is scanned and the other of4 which appears when a light portion of the subject copy is scanned. It Will be assumed for purposes of illustration that when a dark portion of the subject copy I2, such as a letter or a character I4 appearing thereon, is scanned, a frequency in the neighborhood of 1650 cycles will be reproduced, and when the background is scanned, which in this instance is the unmarked` tape, a frequency in the neighborhood of 1150 cycles will be produced. These frequencies will appear in the output of the radio receiver 33 to be amplified in the amplifier 34. It will be understood that the frequency values are selected solely for the purpose of explaining the illustrative embodiment of the invention and that other frequencies may be generated and/ or transmitted. The order of the frequencies may, of course, be reversed.

In the illustrative recorder of Fig. 2, a record blank, such las a recording tape 38, receives markings thereon which correspond to the characters I4 so that a facsimile of the appearance of the subject tape I2 is produced. The tape 38 is guided by idler rollers 39 and 4|)v and is propelled through the printing zone by a drive roller 4| and an idler 42. The drive roller 4| is driven by a motor 46 which may be a synchronous motor connected to an alternating current service connection IIB. Where the motor 46 and the motor I8 are connected to the same synchronized system, it will not, in general, be necessary to transmit separate synchronizing signals. Synchronizing and phasing sign'als may be generated and transmitted as described in the United States patent to Artzt. No. 2,326,740, abovereferred to when this is desir-able or necessary.

The recorder or printer unit comprises a magnetic member or core 52 having a central leg 53 and coil supporting legs 56v and 51. The core 52, for convenience, may be mounted on a suitable base or other support 59. An. armature 62 of magnetic material is movably mounted in any suitable manner so as to complete the magnetic circuit yof the core structure 52 and remain in approximately the central position whenthe recorder is unexcited. This may be accomplished, for example, by employing a torsional mounting spring 6.6 which is secured :at its ends to brackets 64, one of which appears in Fig. 2 of the drawings. The armature 62 is balanced upon and secured to the spring 63, the parts during construction being so arranged that when the magnet structure is unexcitecl, each end of the armature may be spaced an equal distance from its cooperating core leg. The armature 62 thus may have la rocking movement imparted to it which is controlled by the magnetic flux densities in the core legs 56 and l5'I. A straight edge marking blade 6T is formed integrally with or secured upon the armature 62 so as to cooperate with a helical blade or blades 68 on arotatablev printing drum 69. An inlring roller I2 having an ink saturated absorbent periphery 13 bears against the helical blade 68. The rotatable drum 69 land the driving roller 4| may be driven from the motor 46 through a gear device 'I6 similar in function to the gear device 2| of Fig. l o-f the drawings. It will be understood that carbon tnansfer record.-

Cil

ing may be practiced as described hereinafter in connection with Fig. 5 of the drawings.

The magnetic leg 56 of the core 52 is provided. with a coil 19, and the leg 5l is provided with coil 8|. In the illustrative example, the coil I9 is arranged so as to be selectively responsive to the lower frequency signals generated upon scanning thev subject copy. The coil 8| is arranged to be selectively responsive to the higher frequency signals generated upon scanning the subject copy. Selective response is or may be obtained by choosing different inductance values for each coil or by resonating the coils at the desired response frequency by employing the capacitance values of other elements of the system such as the filters to be described.

A high pass filter 83 has the response characteristic indicated by reference character 85 on Fig. 3. A low pass filter 88 has a response characteristic 88, also shown on Fig. 3. In the illustrative arrangement which is designed for the signal frequencies stated above by way of example, tlie low pass filter cuts off at 1800 cycles, and the high pass filter cuts off at 900 cycles. Conversely, attenuation for the low pass filter begins at 900 cycles and at 1800 cycles for the high pass filter. A transformer 9| provides a convenient means for transferring signals from the amplifier 34 to the filters 83 and 88. The transformer is provided with a center tapped secondary 92 so that the center tap serves as a. common connection for the coils of. the recorder structure. The low pass filter 88 is connected with the coil 19 by a connection 94, and the high pass filter 88 is Iconnected to the coil 8| by a. connection 96.

In operation of the printer unit disclosed in Fig. 2 of the drawings, the balanced armature 62 takes the place of a discriminator when fed from suitable filters such as the filters 83 and 88. For example, when a dark portion of the subject copy I2 is scanned, the response of the filter 83 is at the level indicated by reference character 99 on Fig. 3, whereas, the response of the filter 88 is indicated at IDI. The armature 62', therefore, is actuated to bring the tape 38 backed by the printer blade B'I into contact with the printing helix 68. When the white condition is restored, the coil 'I9 will be energized to av greater extent than the coil 8|, and the armature 62 will be maintained in a position such that the tape does not Contact the helix 68. Shading coils in the form of highly conductive rings |03 and |04 act to prevent vibration of the armature 62 at frequencies approaching signal` frequencies thereby to avoid recording of a dot pattern.

Even with the carrier signal applied directly to excite the magnetic circuits of the recorder structure without demodulation, it is to be noted that the marking instrumentality comprising the armature 62 and the printer bar 61 has two definite positions in the illustrative example correspending to the two light reflective conditions of the subject copy I2. This provides clean-cut y recordings with good definition from la frequency modulated carrier, heretofore obtainable only by resorting to a deniodulating process and pushpull amplification with a special amplifier. While the light reiiective properties of the surface of the subject copy have been mentioned, it will be understood that the transmitter pickup may be operated by the light transmitting properties of the subject copy and that image signal reversal maybe employed at the transmittingsta.- tion in either case.

Fig. 5 shows a slight modification of the circuit arrangement of Fig. 3 in which amplification following lter selection is employed. Frequency modulated signals are applied to the primary of a transformer I 06, the secondary of which is connected to a low pass filter |08 and a high pass filter |09. The selected frequencies passed by these two filters are amplified in amplifier tubes ||I and I I2, respectively, so as selectively to excite printer coils 8in, and 19a. These coils are tuned by condensers I4 and I I6 whereby the masnetizing current of each coil will be increased at the signal frequency to which it is to respond. Each coil is included in the plate circuit of its corresponding amplifier tube, and one end of each winding is connected to a source of plate voltage ||8l The plate current owing in each coil or the magnetizing effect of the plate current in each coil may be balanced in any desired manner by tube selection, inclusion of ohmic resistance in each tube plate circuit, or by other known methods so that the associated printer armature, for example the armature |52, is balanced.

Fig. 6 shows a recorder constructed in accordance with the invention for page printing. The general arrangement of the recorder may be as shown diagrammatically in the United States Patent No. 2,326,740, to Maurice Artzt, referred to above or in the United States reissue patent No. Re. 20.152, granted to Charles J. Young on October 27, 1936. The recorder comprises a cylinder |2| which is provided with a raised helix |22 and a printer bar |23. In the illustrative example, the recorder is intended to print continuously upon a web or sheet |26 with means (not shown) for interposing carbon paper between the printer bar and the paper web |26, all as disclosed in the Young reissue patent, No. Re. 20,152. Two magnetic units |28 and |29 are shown for moving the printing bar |23 in response to the received image signals. As the units |28 and |29 are or may be similar, a description of one will suffice for both. The printing unit |28, for example, may be provided with an armature |33 which is mechanically balanced about a pivotal support |34. Mechanical balance may be accomplished by tapering the armature or by loading one end. It is also preferred that the magnetic balance of the armature be maintained. The extended portion |36 of the armature is connected in any suitable manner to the printer bar |23. The signal input arrangement is substantially like that shown in Fig. 2 of the drawings and comprises a high pass filter |39 and a low pass nlter |4| fed from a transformer |42. Where multiple magnetic units are employed as shown in Fig. 5, it is preferable to include means for balancing the magnetic effect of the signal upon each armature, and this may be accomplished as shown illustratively in Fig. 5 by providing two volume control potentiometers |43- and IM. for the marking coils |45 and |45. Similar volume control potentiometers M8 and `Il!!! are provided for the operating coils on the units. It is believed that in view of the foregoing, the operation of Fig. 5 will be understood without further explanation.

' At the transmitter a revolving drum type signal pickup arrangement such as is shown in Fig. 1 of Artzt patent, No. 2,326,740, may be employed for scanning pages of copy for transmission.

Having now described the invention, what is claimed and desired to be secured by Letters Patent is the following:

1. A recorder for producing marks in accordance with applied image signals, comprising an electromagnetic core providing two magnetic circuits, a movable armature associated with said core to complete the magnetic circuits thereof, an exciting coil for each circuit, one of said coils being designed to produce maximum magnetization in one magnetic circuit when excited by image currents of lower frequencies to move the armature in one direction, the other of said coils being designed to produce maximum magnetization in the other magnetic circuit when excited by image currents of a higher frequency to move the armature in another direction, and a marking device associated with said armature.

2. A recording system for producing marks in accordance with image signals repesented by frequency variations of a carrier, comprising a filter for separating the higher frequency components of the carrier, a second filter for separating lower frequency components of the carrier, a recorder, control means in said recorder having an operative connection to said high pass filter, additional control means in said recorder having an operative connection to said low passlter, and a movable recording instrumentality operative to be moved selectively in response to both control means to produce marks on a recording sheet.

3. Apparatus for producing a copy of a picture, drawing, or other subject matter in facsimile on a record surface, comprising a facsimile copying device responsive to an alternating current, the frequency of which varies in accordance with the elemental areas of the subject matter to be recorded, means to cause the copying device to scan the record surface, and means for applying separated components of the frequency` modulated current to the copying device, said copying device being responsive once at the time of application of one separated frequency component and being responsive again when the application of the separated component ceases and at the time of application of another separated frequency component.

4. Apparatus for producing a copy of a picture, drawing, or other subject matter in facsimile on a record surface, comprising a facsimile copying device having a plurality of means responsive to an alternating current, the frequency of which varies in accordance with the elemental areas of the subject matter to be recorded, means to cause the copying device to scan the record surface, means for applying separated components of a given frequency of the frequency modulated current to the alternating current responsive means, said copying device moving once at the time of application of a separated frequency component to one of said alternating current responsive means and moving again at the time of application of another separated frequency component to another of said alternating current responsive means.

5. A facsimile recording system for providing marks in accordance with image signals represented by frequency variations of a carrier, com- `prising a balanced electromagnetic rec-order, a pair of operating coils for said recorder, a condenser sliunlted across each coil to increase the response of the coil to carrier current of a given frequency, a pair of lters, means for applying the signal modulated carrier to said filters, and means operatively connecting each filter to the coil having maximum frequency response at the filtered frequencies.

6. A recorder for recording image signals comprising .a balanced electromagnet, balance being obtained by subdividing said electromagnewl-l into markingv engagement with said record surface yupon,energization of the other of ksaid coils by alternatingv current of. adiiferent frequency.

7.:,A `,facsimile recordingv system for providing :marks iny accordancewith image signals repre- .sented fby frequency'variations of. a carrier, com- .vlprising a balanced.electromagnetic recorder, a pair of operating: coils for said recorder, means associatedr with-each coil to increase the response ofthe coilto carrier current of a given frequency, a pair vof filtersymeansj for applying the signal .modulated carrier to said filters, and means opv: eratively connecting each iilter to the coil having maximum frequency response at the ltered frequencies.

8.'A recorder for providing marks in accordance'with markingand spacing signals, comprisring. a'plurality of balanced electromagnetic units, a pair `of .operating coils for each unit, means to :fprovide marking signals to the marking coils of each recording unit as a group, means to lprovide vspacing'signals for the spacing coils of each electromagneticlunit as ,a group, and volume con- 18 trolimeans interposed inthe connection to one .of the group of coils whereby to assist in maintaining balance of the electromagnetic units to marking and spacing signals.

9. A recorder. for providing marks in accordance 'with image sign-als represented by frequency variations of a carrier, comprising a marking` device, 'a plurality of balanced electromagnetic units operatively yconnectedV to said marking device, a pair of operating coils for each unit, means to` lprovide marking signals to the marking coils of each recording unit, means to provide spacing signals for the spacing coils of each electromagnetic unit, and volume control means interposed in the connection to each group of coils whereby to assist in maintaining balance of the electromagnetic units to marking and spacing signals.

CHARLES J. YOUNG.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,500,785 Alexanderson July 8, 1924 1,914,898 Schroter June 20, 1933 1,959,016 Applegate May 15, 1934 2,075,604 Finch Mar. 30, 1937 2,205,450 Wise June 25, 1940 2,212,447 Mathes Aug; 20, 1940 2,222,937 Dimmick Nov. 26, 1940 2,269,594 Mathes Jan. 13, 1942 A2,326,740 Artzt Aug. 17, 1943 

